1. Technical Field
The present invention relates generally to a filter media. In particular, the present invention relates to a filter media that carries a HEPA rating after it is pleated and that is capable of repeatedly being easily cleaned for reuse.
2. Description of the Prior Art
Filter media that carries a relatively high efficiency rating commonly referred to as a High Efficiency Particulate Air (HEPA, 99.97% efficient at a 0.3 xcexcm particle size) filter rating is known. For example, U.S. Pat. Nos. 4,877,433 and 5,507,847 disclose filter media including a porous membrane made from expanded polytetrafluoroethylene (ePTFE) with a HEPA filter rating. The filter media can be pleated. It has been found that a HEPA rating is difficult to obtain after a pleating operation because cracks or tears can be introduced into the membrane. These cracks and tears can provide a location for little or no filtration to take place and a reduction in total filtration efficiency of the media.
To prevent such cracking or tearing damage, the ePTFE membrane is typically xe2x80x9csandwichedxe2x80x9d between two sheets of material that protect the ePTFE membrane during a pleating operation. However, such protective sheet material often collects the particulates being filtered and does not easily release the majority of the particulates. at least not without significant effort or measures.
The present invention is directed to a cleanable pleated filter media that has a HEPA filtration rating. The filter media comprises a porous primary filtration layer tending to be less than HEPA rated, especially after experiencing damage during a pleating operation. A first substrate layer is attached to the primary filtration layer to maintain the shape of the filter media. The first substrate layer comprises a non-woven filtration media that is less than HEPA rated. A second substrate layer is attached to the first substrate layer to serve as a secondary filter at areas of the primary filtration layer that may become damaged. The second substrate layer comprises a non-woven filtration media that is less than HEPA rated.
The porous primary filtration layer comprises an expanded polytetrafluoroethylene membrane. The filter media is pleated and retains a HEPA rating. The porous primary filtration layer is bonded to the first substrate layer. The first substrate layer is adhesively or thermally bonded to the second substrate layer.
The first substrate layer is made from a spun bond material of a weight in the range of 0.5 oz./sq. yd. to 12 oz./sq. yd and selected from the group including polyethylene terephthalate (PET) polyester, polyphenylene sulfide (PPS), or polypropylene (PP), a bicomponent fiber with a polybutylene terephthalate (PBT) sheath and a polyethylene terephthalate (PET) core and a bicomponent fiber with a polyethylene terephthalate (PET) core and a polyethylene (PE) sheath. The second substrate layer is made from melt blown material of a weight in the range 0.25 oz./sq. yd. to 5.0 oz./sq. yd. and selected from the group including glass, polypropylene (PP), polybutylene terephthalate (PBT), polyphenylene sulfide (PPS), ethylene-chlorotrifluorethylene (ECTFE), polyethylene terephthalate (PET) polyester and polyethylene (PE). The filter media has an air flow regeneration of at least 99% immediately subsequent to being cleaned by loosening accumulated particulates from a filtering surface of said primary filtration layer.